Magnetic hyperfine fields in Y2Fe17−x Si x compounds

Y₂Fe_17–x Si _x compounds withx=0, 0.5, 1.0, 1.5, 2.0, 2.5 and3.0 were investigated by magnetic measurement andNMR. It is found that with increasing Si content the Curie temperatureT _C increases while the average Fe magnetic moment _Fe decreases. NMR study indicates that Si preferentially substitute the Fe atoms at 4f sites, which is responsible for the increase ofT _C.     

Magnetic properties of (GdxY1−x)Co2B2 compounds

Magnetic measurements were performed on the (Gd_xY_1−x)Co₂B₂ compounds, in the temperature range 2–800 K and fields up to 70 kOe. YCo₂B₂ is a paramagnet. The (Gd_xY_1−x)Co₂B₂ compounds with x≥0.2 shows a ferromagnetic type ordering. The saturation magnetization at 2 K coincides only with the contribution of gadolinium. The Curie temperatures are nearly linearly dependent on the composition. Above the Curie points, the thermal variations of the magnetic susceptibility can be described as a superposition of a temperature independent term ϰ₀ on a Curie-Weiss behavior. The Curie constants are determined by the contribution of Gd³⁺ ions only. The ϰ₀ values increase when the gadolinium content is greater. The observed properties are discussed in the wider framework of the magnetic behavior of cobalt in GdCo_xB_y compounds.     

Structure,magnetic properties and magnetocaloric effects of Fe50Mn15−x Co x Ni35 alloys

Fe50Mn15-xCoxNi35(x=0,1,3,5,7)alloys were prepared by arc melting under purified argon atmosphere.The ingots were homogenized at 930°C for 90h followed by water quenching.The crystal structure,magnetic properties and magnetocaloric effects of the alloys were studied by X-ray diffraction(XRD)and MPMS-7-type SQUID.The results show that all samples still maintained a single-(Fe,Ni)-type phase structure.With the increase of the content of Co,the Curie temperatures of these alloys increased and exhibited a second-order magnetic transition from ferromagnetic(FM)to paramagnetic(PM)state near Curie temperature.The maximum magnetic entropy change and the relative cooling power of Fe50Mn10Co5Ni35alloy was 2.55 J/kg·K and 181 J/kg,respectively,for an external field change of 5T.Compared with rare earth metal Gd,Fe50Mn15-xCoxNi35 series of alloys have obvious advantage in resource price;their Curie temperatures can be tuned to near room temperature,maintain a relatively large magnetic entropy change at the same time and they are a type of potential magnetic refrigeration materials near room temperature.     

Magnetic properties of U (Fe x Al1−x )2 and U(Fe y Ni1−y )2 compounds

The results of magnetic measurements and ferromagnetic resonance studies performed on U(Fe _x Al_1–x )₂ and U(Fe _y Ni_1–y )₂ compounds over a large temperature range are reported. The saturation magnetization decreases nearly linearly when substituting Fe by Al or Ni. In the composition range x<0.84 and y<0.81, the compounds are Pauli paramagnets, except in the region with y0.10. For UNi₂ two types of magnetic behaviours are shown. This compound can be both a ferromagnet withT _c =23.5 K and a Pauli paramagnet, depending on the crystal structure. Above the Curie temperatures, the reciprocal susceptibility for the compounds with x>0.84 and y>0.81 obeys a temperature dependence of the formX=X _o+C(T-) ^–1. The effective iron moments decrease when substituting iron by nickel or aluminium. The ferromagnetic resonance measurements show that theg values are not composition-dependent. A linear variation of the mean iron magnetization with the exchange field is observed. Finally, the magnetic behaviour of iron in these compounds is analysed.     

Magnetic properties of (Mn1 − x Fe x )1.68Sn solid solutions

Solid solutions in the (Mn_{1 ? x} Fe _x )_1.68Sn system (x ≤ 0.5) with a Ni₂In-type structure are synthesized by the solid-phase reaction method in a stepwise temperature regime. The unit cell parameters a and c decrease with an increase in the iron concentration in the alloys and become equal to a = 0.430 nm and c = 0.538 nm for the (Mn_0.5Fe_0.5)_1.68Sn alloy. A superstructure with the unit cell parameters a _ss = 3a and c _ss = c is revealed in alloys of the system under investigation. The specific magnetization of the alloys increases nonlinearly from 53 G cm³ g^?1 in the Mn_1.68Sn alloy to 72 G cm³ g^?1 in the (Mn_0.5Fe_0.5)_1.68Sn solid solution. The Curie temperature changes from 270 K in the initial alloy of the composition Mn_1.68Sn to 365 K in the alloy of the composition (Mn_0.5Fe_0.5)_1.68Sn. All solid solutions in the (Mn_{1 ? x} Fe _x )_1.68Sn (x ≤ 0.5) system exhibit metallic conductivity in the temperature range from 77 to 450 K.     

Magnetic phases in quasi-binary (Fe1−x Cox)Ge2 intermetallic compounds

Magnetic neutron diffractometry revealed the existence in (Fe_1−x Co_x)Ge₂ solid solutions (x<0.5) with C16 structure of only two magnetic phases, namely, low-temperature (AFI) and high-temperature (AFII). A third magnetic phase, AFIII, suggested by earlier magnetic measurements, has not been found. The AFI and AFII phases have a commensurate and an incommensurate antiferromagnetic structure with the wave vectors k ₀=2π/a (1,0,0) and k=k ₀+δ k, respectively. The regions of their existence are shown in the magnetic phase diagram. Neutron diffraction measurements yielded the concentration dependence of the average magnetic moment per atom in the antiferromagnetic sublattice of a 3d metal, which, similarly to the dependence of the Néel point on x, was found to be nonlinear. An analysis of these dependences suggests that substitution of cobalt for iron is accompanied, on the one hand, by a decrease of the local spin density on the iron atoms in the nearest environment of a cobalt atom and, on the other hand, by an increase of the effective exchange integral between the nearest-neighbor iron atoms located along the tetragonal axis. Fiz. Tverd. Tela (St. Petersburg) 41, 283–289 (February 1999)     

Magnetic properties and microstructure of Sm2Fe17−xTax compounds

The magnetic properties and microstructure of cast and annealed Sm₂Fe_17−xTa_x (0 ≤ x ≤ 2) alloys were investigated by means of microstructural, X-ray diffraction and thermomagnetic analysis. A process for obtaining the Sm₂Fe₁₇ phase nearly free of iron in the as-cast state is described. The method consists of adding 5 at% of Ta to the melt. By this addition of Ta to the basic alloy, a two phase structure of the as-cast ingots consisting of Sm₂Fe₁₇ phase and a Pauli paramagnetic hexagonal Laves phase - TaFe₂, can be obtained. X-ray diffraction showed an increase of the lattice spacing dependent upon the tantalum concentration in the alloy, which indicated some solid solubility of Ta in the Sm₂Fe₁₇ phase. Quantitative electron probe microanalysis confirmed the solid solubility of tantalum in the Sm₂Fe₁₇ phase of up to 2.3 (± 0.5) at%. This resulted in an increase of the Curie temperature of the Sm₂Fe_17−x phase, which was determined by means of thermomagnetic analysis.     

Mössbauer investigation of the57Fe hyperfine field in Y(Fe1−xCCo x )3 intermetallic compounds

The⁵⁷Fe magnetic hyperfine fieldH _hf at 77 K and 293 K and the lattice parametersc anda of the intermetallic compound Y (Fe_1?x Co _x )₃ have been investigated as a function of the Co concentration for 0.0≤x≤0.99 by Mössbauer spectroscopy and X-ray diffraction, respectively. The magnetic hyperfine fieldH _hf shows a Slater-pauling type concentration dependence with a maximum atx=0.4 and a strong decrease towards high Co concentrations.     

Magnetic resonance of the M x Mn1 ? x S compounds (M = Cu, Cr)

Cation-substituted manganese monosulfide M _x Mn_{1 ? x} S (M = Cu, Cr) has been investigated using the electron paramagnetic resonance method. The temperature and concentration dependences of the width and shape of the magnetic resonance line have been considered using the Van Vleck method of moments. It has been shown that, if the Mn²⁺ ions are substituted by the copper and chromium ions, the change of the effective exchange interaction in the system that substantially affects the magnetic resonance spectra takes place.     

Magnetic properties of amorphous Mn x B100−x alloys

Magnetic properties of amorphous Mn _x B_100–x alloys ranging fromx = 30 to 70 under high magnetic fields and low ac magnetic fields in the temperature range from 4.2 K to room temperature have been investigated. Samples which have Mn concentrations of aboutx = 40–60 show spin-glass-like properties in the low-temperature region. This spin-glass characteristics result from a frustration in the spin system which is caused by the competition of ferromagnetic and antiferromagnetic interactions between randomly distributed Mn atoms. Both magnetization at 4.2 K and paramagnetic momentP _eff as a function of Mn concentration show a peak aroundx 44 which drops rapidly towards both sides of the Mn content.     

Structure and magnetic properties of the intermetallic La2Co17−xMox (x=0.5, 1, 1.5, 2) and La2Co16−yFeyMo (y=0, 1, 2, 3, 4, 6) compounds

The effect of Mo and Fe atoms on the crystal structure and magnetic properties of the intermetallic La₂Co_17−xMo_x (x=0.5, 1, 1.5, 2), and La₂Co_16−yFe_yMo (y=0, 1, 2, 3, 4, 6) compounds have been studied by X-ray diffractometry, magnetic measurements and Mössbauer spectroscopy. All samples belong to the rhombohedral Th₂Zn₁₇-type structure and their lattice parameters a and c increase both with Mo and Fe content. From the La–Co–Mo samples only the one with x=0.5 presents planar anisotropy, whereas from the La–Co–Fe–Mo samples only the y=1 has uniaxial anisotropy. The magnetization M_S and the Curie temperature T_C decrease upon Mo substitution, whereas the anisotropy field H_A does not change significantly. In the Fe-substituted compounds M_S increases, but the Curie temperature increases slightly for 0⩽y⩽4 but decreases in y=6. The low temperature M–T curve shows that the samples La₂Co_16.5Mo_0.5, and La₂Co₁₀Fe₆Mo present a spin reorientation transitions at 70 and 260 K, respectively. Mössbauer samples were obtained for all Fe-containing samples in the temperature range 20–300 K. Above 260 K a jump in the values of the hyperfine fields and quadrupole splitting parameters is observed which can be associated to the spin reorientation.     

Magnetic properties of RNi1−xIn1+x (R=Gd–Er) compounds

AC and DC bulk magnetic measurements were performed for RNi_1−xIn_1+x (R=Gd–Er and x=0,0.1, 0.25) compounds. These compounds crystallize in the hexagonal ZrNiAl-type structure. The lattice parameters a and c for the RNiIn series decrease linearly with increasing number of 4f electrons. For nonstoichiometric RNi_1−xIn_1+x additional indium atoms occupy the 2(c) crystallographic site and the a parameter increases while the c parameter decreases with increasing indium content. The stoichiometric samples show ferromagnetic behavior with the critical temperature changing from 96 K for R=Gd to 9 K for R=Er. In the nonstoichiometric RNi_1−xIn_1+x compounds increase in the indium content leads to decrease in the ferromagnetic critical temperatures and to a change of the antiferromagnetic ordering for x=0.25 in the case of R=Dy, Ho and Er.     

Magnetic and electrical properties of (Ni0.8Cu0.2)1−x Cox Mn0.02Fe1.9O4 ferrites

The effect of Co substitution on the magnetic and electrical properties of iron-deficient nickel–copper mixed ferrites containing a small quantity of manganese oxide was investigated. The presence of Co enhances the specific magnetization although the saturation magnetization falls a little due to decrement of density. The initial permeability changes linearly with the average grain size of the materials and shows fairly good thermal stability for higher Co concentration. An appreciable increment in DC resistivity along with decrement in dielectric loss factor at 100 MHz can also be obtained for higher Co concentration.     

Mössbauer Study of the Soft Magnetic Nanocrystalline Fe81−x Ni x Zr7B12 (x=10–40) Alloys

Hyperfine Interactions - Formation of the soft magnetic nanostructure in amorphous Fe81?x Ni x Zr7B12 (x=10–40) alloys due to heat treatment is studied by the Mössbauer, DSC and...     

Calculation of the electronic structure and hyperfine fields for Fe1 − x Co x B and (Fe1 − x Co x )2B compounds by the Korringa-Kohn-Rostoker method

The magnetic properties of Fe_{1 ? x} Co _x B and (Fe_{1 ? x} Co _x )₂B disordered compounds were investigated using first-principles calculations of the electronic structure in the framework of the density functional theory with the Korringa-Kohn-Rostoker method. The concentration dependences of the magnetic moments and the electron density were calculated for the Fe_{1 ? x} Co _x B solid solutions. The results obtained were used to analyze in detail and to interpret the transition from a magnetic phase to a nonmagnetic phase, which was previously revealed from the experiments in the compounds under investigation. The performed analysis of the calculated hyperfine fields induced by the electronic shells at the iron and cobalt atoms in the (Fe_{1 ? x} Co _x )₂B borides made it possible to explain the experimentally observed magnetic anisotropy.     

Magnetic properties of Fe−Mn−Al alloy system in the FCC disordered phase

In this work we report the experimental studies of Fe?Mn?Al alloys in the FCC disordered phase at room temperature by Mössbauer spectroscopy and X-ray diffraction. In this phase the alloys are antiferromagnetic with a constant mean hyperfine field ( \(\bar H\) ) near 26 kOe in the composition range from 0 to 7.5 at.% Al and 50 to 65 at.% Fe. When the Al or Fe concentration increases, the \(\bar H\) value gradually decreases to zero and the alloy becomes paramagnetic. In the same way when the Al concentration increases the lattice parameter increases linearly but when the Fe concentration increases the lattice parameter remains nearly constant for alloys with 5 at.% Al and decreases for alloys with 10 at.% Al.